In the semiconductor industry, TaSixNy films have been extensively studied as a barrier layer for Cu interconnects and as a bottom electrode for DRAM capacitors. Such films typically exhibit low resistivity and excellent thermal/chemical stability against high temperature processing. TaSixNy films have been reported in the literature to be excellent copper diffusion barriers up to 900° C.
In addition to applications as a barrier layer or as a bottom electrode, TaSixNy films have recently been investigated as a metal gate electrode due to their good thermal stability and appropriate work functions for n-type metal-oxide semiconductor devices.
With decreasing semiconductor device dimensions, a highly conformal diffusion barrier deposition is required. Additionally, for metal gate electrode purposes, a low damage deposition method is needed. For this, the sputtering of TaSixNy films is not an adequate technique since sputtering typically does not provide sufficient conformality. In sputtering, a target(s) of the desired material(s) is bombarded with excited ions that knock atoms from the target(s). These atoms are then deposited on a surface. Thus, the sputtering mechanism makes it difficult to provide highly conformal diffusion barriers in high aspect ratio applications and dielectric damage free gate electrodes.
Alternative techniques such as chemical vapor deposition (CVD) have been employed in forming TaSixNy films. In a typical CVD process, a solid film is formed through a chemical reaction, e.g., pyrolysis, photolysis, reduction, oxidation or reduction and oxidation (redox), of a gas mixture. A wafer surface or its vicinity is heated to high temperatures in order to provide additional energy to the system. CVD can be problematic in that it exhibits one of the following drawbacks: poor conformality; excessive silicon consumption; high preparation and growth temperatures; and selectivity loss.
In view of the state of the art mentioned above, there is a need for providing a deposition method that is capable of forming metallic films with high conformality, low growth temperatures, easily controlled thickness, atomic layer composition, large area uniformity, low impurity content, minimal dielectric damage and little or no silicon consumption. There is also a need for providing thin metallic films, on the order of a few monolayers or less, which can be used in fine feature applications.